1. Field of the Invention
The present invention relates to a nitrite-type nitrification carrier and a method for producing the same and a method and an apparatus for removing nitrogen using the same, and relates to a technology for removing ammonium in water and in the atmosphere by a nitrite-type nitrification reaction.
2. Description of the Related Art
Biological treatment of wastewater and sewage with microorganisms has been widely used because of its relatively low cost. However, some type of microorganisms have slow growth rate, are easily poisoned, or are difficult to multiply in some environment, so that the biological treatment is sometimes not an effective method. Therefore, a treatment method has become commercially practical in which the biological treatment is carried out by using an immobilized microorganism carrier in which a specific microorganism is previously entrapped and immobilized in order to positively form the environment where the microorganism is easily propagated.
Gel materials are typically used for the immobilizing material for supporting (holding) microorganisms inside them. The requirement for these materials includes being harmless to natural environment, no change of properties or not being decomposed by microorganisms, having high mechanical strengths, being capable of supporting microorganisms in sufficient abundance and the like. The gel materials which have become commercially practical include a polyethyleneglycol-based polymer described in Japanese Patent No. 1630654, a polyvinyl alcohol-based resin and the like. As for the microorganisms to be entrapped and immobilized in the gel material, nitrifying bacteria that oxidize ammonium are mainly used, and the sources of the microorganisms are the activated sludge from a sewage-treatment plant or microorganisms which are grown axenically.
When ammonium in wastewater is to be removed using a conventional immobilized microorganism carrier in which the nitrifying bacteria are entrapped and immobilized, ammonium is oxidized to nitrate, which is a final oxidized product, through nitrite in aerobic conditions. This nitrate is converted to nitrogen gas and water by denitrifying bacteria in anaerobic conditions to remove nitrogen.
However, the conversion from nitrate to nitrogen gas using the denitrifying bacteria needs the addition of organic matter such as methanol, which has the drawback of increasing running cost. Therefore, a method for removing nitrogen that requires the addition of only a small amount of organic matter has been desired.
As a method for removing nitrogen which solves this drawback, the SHARON-ANAMMOX reaction process has been developed in which the oxidation of ammonium is stopped midway so that about halves of nitrite and ammonia, respectively, remain after the denitrification. However, it is extremely difficult to control the reaction so as to allow about halves of nitrite and ammonia, respectively, to remain, and the process has hence the drawback of easily resulting in a large amount of nitrate, which is the final oxidized product.
Thus, the present state of the art is that either of the conventional immobilized microorganism carrier and the SHARON-ANAMMOX reaction process have not yet solved the problem of decreasing the quantity of the organic additive to reduce the running cost.